In many groundworking and material handling machines, there generally is provided a mobile support frame mounted on wheels or track units, a rotatable platform mounted on the support frame on which there is provided an operator's station and a boom mounted on the platform and angularly displaceable about a horizontal axis. Typically, the front end of the machine further is provided with a handle or dipper stick pivotally connected to the free end of the boom and some form of groundworking or material handling assembly mounted on the free end of the handle or dipper stick. Such assemblies typically consist of an excavator bucket, a rake, a pair of jaws such as in a grapple or sets of shears or crushers and the like. In most of such constructions, the boom, handle or dipper stick and the assembly mounted on the handle or dipper stick are pivoted by hydraulic cylinder assemblies. In some applications, where the working assembly consists of a pair of jaws, it is common to provide for the pivotal movement of both jaws, the pivotal movement of only one jaw and the fixed positioning of the other jaw or the pivotal movement of one jaw and the fixed positioning of the other jaw but the angular adjustment of the position of the fixed jaw.
In one common attachment for machines of the type described, there is provided at least a lower jaw member sometimes referred to as a "thumb" pivotally connected to the underside of the handle of the machine, a hydraulic cylinder assembly operatively interconnecting the underside of the handle and the lower jaw member for angularly displacing the lower jaw member relative to the handle, and often an upper jaw member in the form of a bucket, grapple jaw, shear blade, rock crushing jaw, rake or the like, pivotally connected to the handle, in which the lower fixed jaw member may be used independently of or in cooperation with the upper jaw to perform various work functions.
In the type of attachment described, in adjusting the angle of the lower jaw member relative to the handle, it has been the common practice in the prior art simply to operate certain controls at the operator's station on the machine to supply and withdraw fluid to and from opposite ends of the cylinder assembly interconnecting the handle of the machine and the lower jaw member to extend or retract the rod portion thereof, correspondingly adjusting the angle of the lower jaw member, and then blocking the flow of fluid to and from the opposite ends of the cylinder assembly to lock the rod portion thereof and thus provide a strut of a fixed length.
Such type of arrangement, however, is relatively costly to manufacture in that it requires running fluid supply and return lines from the platform of the machine along the boom and handle to the cylinder assembly for the lower jaw member. Such fluid supply and return lines and the various fittings required add considerably to the cost of such attachments. Furthermore, such lines are vulnerable to damage and require periodic maintenance.
It thus has been found to be desirable to provide the type of attachment as described which not only provides for an expeditious angular adjustment of the lower jaw member and a rigid strut therefor for withstanding substantial loads imposed thereon in performing various work functions but further an avoidance of the relatively high manufacturing costs and potential maintenance problems inherent in comparable prior art attachments.